You are mixing multiple interrelated ideas (and to be fair so was the person you are replying to). In most cases the "claim of negation" is the default positio

You are mixing multiple interrelated ideas (and to be fair so was the person you are replying to). In most cases the "claim of negation" is the default position (related to the null hypothesis). If I claim there are invisible faeries that hold us to the earth. The negation of that claim is that there aren't. But this sort of reasoning only applies to things like debate and philosophy. Science is fine with the unknown, claims must meet the burden of proof to be considered more than a speculation. Hence a "claim of negation" isn't scientific, because you instead present observation and calculation which makes the claim invalid in the first place. The default state being that no claim (we call these hypothesis) is valid. Sometimes this means that there are many competing partially valid hypothesis. One can't prove a negative, so instead science deals in hypothesis and only ever judges the positive claim against what we know. I can't emphasize this enough, there is no such thing as a negative claim in science: just a claim that we don't know the answer yet because no current hypothesis are convincingly valid. People aren't claiming it's an asteroid, because that has a specific definition it doesn't match. Note in the article he talks about comets as one thing some people think it is. In the title of the article it's "Interstellar Object" which I don't think anyone is disputing. The hypothesis he is putting forward is reasonable though. At least as well as any other hypothesis. We don't really have proof (observations) either way (and like a good scientist he spends a lot of time pointing out how we should be ready next time) so no hypothesis can meet a burden of proof at the moment. But then science doesn't really use a concept of "burden of proof", that's a legal concept. Instead we simply work with our least wrong models - even our best theories are not proven - which are judged by how well they predict the world. And in this example the hypothesis "aliens did it" answers a lot of questions in a reasonable way. But then so does "nature did it" but some of the answers and mechanisms are less convincing in that case. And I think the point the interviewee is making is that we should be ready to better answer that question next time an object like this comes by because the answer "nature did it" is somewhat unconvincing for this object.